Electrostatic paint spray



Jan. 16, 1962 J. T. MARVIN ELECTROSTATIC PAINT SPRAY Filed Aug. 26, 1958Hi HIHHHHHHIHHIHH Fig. 6

btates This invention relates to electrostatic coating operations and isparticularly concerned with a method and apparatus for electrostaticallydispersing coating material in a predetermined pattern.

It is an object of the invention to provide a stationary coatingmaterial dispersing unit which will disperse coating material such aspaint in a predetermined pattern therearound.

In carrying out this object, it is a further object to provide astationary container of a predetermined shape and having a substantiallycontinuous lip therearound wherein all portions of the lip lie in thesame horizontal plane whereby paint supplied to said container inquantities sufiicient to overflow the lip portion thereof iselectrostatically dispersed simultaneously from all lip portions and isdeposited upon articles spaced therefrom when opposite electrostaticcharges are impressed on the container and the articles.

Another object of the invention is to provide a method forelectrostatically dispersing coating material such as paint from astationary container whereby a predetermined paint pattern may beestablished without moving parts.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawings wherein preferred embodiments of the present invention areclearly shown.

In the drawings:

FIGURE 1 is a plan view of one type of electrostatic paint sprayapparatus as used in connection with the present invention.

FIGURE 2 is a view in section on line 22 of FIG- URE 1 and showing anarticle being painted.

FIGURE 3 is a fragmentary view of one of the lip portions of the deviceshown in FIGURE 4.

FIGURE 4 is a view taken on line 44 of FIGURE 3.

FIGURE 5 is a plan view of another type of apparatus shown in connectionwith a conveyor which is diagram matically depicted.

FIGURE 6 is a plan view of still another type of apparatus.

FIGURE 7 is a view of the device shown in FIGURE 6 taken in thedirection of the arrow marked 7 thereon.

Electrostatic coating apparatus as heretofore described generallycomprises a moving element, such as a centrifugal distributor, fordistributing the coating material in an expanding circular pattern. Thisdistributor is charged electrostatically and the coating material, suchas paint, when it is thrown from the distributor, is simultaneouslycharged, atomized and dispersed electrostatically. The charged particlesthereof are attracted to the article to be painted which carries anopposite charge to the charge on the particles. One of such distributorsis clearly described in copending application S.N. 687,107, now PatentNo. 2,975,755 and assigned to the assignee of the present invention. Thedistributor used in connection with the present invention will likewiseprovide an expanding circular pattern of paint, as desired, but, due tothe peculiar nature thereof, involves no moving parts. Further, bychanging the shape of the distributor, it is possible to providepatterns of varying shape as desired.

Referring specifically to the drawings, FIGURE 2 shows a section of adistributor as shown in plan view in FIG- URE 1. This distributor isessentially a circular con- Jatent U T 3,017,114 Patented Jan. 16, 1962tainer or cup 20 supported upon a dielectric base 22 and including apaint supply tube 24 extending preferably centrally therein. Around theedge of the container 20 is a lip 26 which is substantially horizontalin extent wherein all portions of the lip 26 lie in the same horizontalplane. The container 20 may be made from metal, or nonconductingmaterial, and is connected to one side of an electrostatic power source30, the other side of which is connected to a hanger 32 which supportsand is electrically connected to an article 34 to be painted. Thus, thecontainer 20 and the article 34 have impressed thereon oppositeelectrostatic charges.

In operation of the device, paint or other suitable coating material issupplied through the tube 24 to the container 20 as by pump or gravityfeed and the tube 24 in this instance is preferably formed from amaterial having high dielectric strength such as polytetrafiuoroethylene(Teflon), polyethylene, polymonochlorotrifluoroethyl (Kel-F), etc. Whenthe paint fills the container 20, it will overflow substantiallysimultaneously from all portions of the lip 26. The quantity of overflowmay be controlled by controlling the quantity of incoming paint and ispreferably maintained in a thin film to provide the most desirabledispersion of paint therefrom. As the paint overflows the lip, it isdistributed, atomized and electrostatically charged. That is to say, thepaint, as it overflows the lip 26, is electrostatically dispersed in afine mist wherein each particle bears an electrostatic charge oppositeto the charge carried by the article 34 so that the charged particles ofpaint are attracted to the surface of the article 34 which bears theopposite charge. Obviously, since the container 20 is circular, itprovides an expanding circular pattern of paint whereby articles spacedor conveyed therearound will be coated.

A modification of this structure is shown in FIGURE 3 wherein aplurality of depressed lip portions 36 are provided around the peripheryof the container 20. These lips take the form shown in section in FIGURE4 and may be closely spaced around the cup to provide a plurality ofseparated jets of paint spray. Obviously, these jets, due to the normalpattern of the atomized paint, will join into a continuous expandingpattern at some distance from the distributor whereby the same resultsare ob tained in connection with the device shown in FIGURE 2. Thepresent modification provides a substantially continuous discharge edgesince the spacing of the several lips 36 is preferably about equal tothe width of the lips. It is apparent, however, that fewer lips may beused if desired although, for most purposes, a rather completeatomization around the edge is most desirable. This modificationsimplifies flow control to a degree. I

Modifications of the present invention permit unique distribution ofpaint in that paint can be projected outwardly of the container in aplurality of separated fields if desired. For example, in connectionwith FIGURE 5, a square container 50 is shown wherein the cornerportions 52 are preferably built up slightly higher than the straightside portions 54 thereof. In this connection, therefore, the paint isdistributed or projected in four directions to provide four fields ofspray, each oriented from the adjacent fields. This permits the use, forexample, of a square conveyor as shown at 56 wherein the articles 58 tobe painted pass around the four sides of the distributor or container 50and are equally painted at each of the four sides. It is apparent toothat, should it be desired to blank out the entry side of the conveyoras noted at 60, the side 62 may be higher than the other three sideswhereby no spray is provided at this side only of the device.

In FIGURE 6, the triangular paint distributor 70 is shown wherein paintis distributed in three disconnected fields as noted by the dot-dashlines. Here again, the

3 corner portions 72 are preferably slightly higher than the main sideportions as shown in FIGURE 7 which is a view taken in the direction ofthe arrow 7 in FIG- URE 6. Of course, it is understood that these highercorner portions are not necessarily required in order for the device tofunction although it is generally desirable to separate the distributioninto uniform fields as shown.

From the foregoing, it is apparent that many modifications of thepresent invention may be made without departing from the spirit thereof.In other words, any shape distributor or container may be used such as ahexagonal container, a generally clover-leaf-shaped container, etc.,whereby the density of paint distributed on articles that are beingtransported therearound on a conveyor may be fully controlled by theshape of the distributor and the shape of the conveyor used therewithwhich permits very flexible operation. Furthermore, a single device maybe utilized which includes adjustable side walls whereby portions onlyof the device may be used as desired. For example, in the circularcontainer, it is possible to have an adjustable side wall that willblock out any desired portion of the lip whereby a semicircle of activelip only is used or a quarter of a circle is used. In this manner,considerable flexibility of the device may be realized while not addingappreciably to the cost thereof. Furthermore, the cost of the device,since no moving parts are involved, is extremely low and the functionthereof is extremely economical and effic'ient.

I In practice, a circular container 12 inches in diameter and one andone-half inches deep at the lip portion has been used to coat articleswith a solvent-containing paint maintained eighteen inches from the lipthereof. In this instance, an electrostatic power unit with an output offrom 90,000 and 100,000 volts was utilized.

It is also apparent that suppressor electrodes may be used to moreclosely direct the path of the distributed paint. Such suppressorelectrodes are clearly shown in copending application S.N. 726,450assigned to the assignee of the present invention.

While the embodiments of the present invention as herein disclosedconstitutepreferred forms, it is to be understood that other forms mightbe adopted.

What is claimed is as follows:

1. In a method for spraying a coating material in a plurality ofseparated patterns simultaneously from a common source, the steps of;supplying coating material to a stationary container, providingseparated lips on said container extending upwardly and in differentdirections from a central point all having the same height and being ofsubstantial extent wherein the longitudinal extent of all of the lips isin the same horizontal plane, overflowing simultaneously coatingmaterial from said container over all of said lips, and simultaneouslyimpressing an electrostatic charge on the container lips whereby thecoating material as it passes over the lips is dispersed, atomized andcharged solely by electrostatic forces into separated spray patternsexpanding outwardly around said central-point.

2. In a method for electrostatically distributing a liquid coatingmaterial in a plurality of fields oriented in diiierent vertical planesaround the central point wherein the coating material for all operationsis contained in a single container, the steps of; providing a stationarycentral container having separated upwardly extending contiguous lipportions disposed in the same horizontal plane and oriented from oneanother, supplying liquid coating material to the container,simultaneously overflowing the coatingmaterialfromthe container and overall of said lips while preventing fluid flow at the junctions betweensaid lip portions and simultaneously charging the container with anelectrostatic charge whereby particles of coating material areelectrostatically atomized from said lips into separated fields ofcoating material sprays and around said container.

References Cited in the file of this patent UNITED STATES PATENTS2,049,940 Barthel Aug. 4, 1936 2,808,343 Simmons Oct. 1, 1957 2,899,136Reindl Aug. 11, 1959 V FOREIGN PATENTS 521,794 Belgium Aug. 14, 19531,004,084 Germany Mar. 7, 1957

